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EclipseLink/UserGuide/JPA/Basic JPA Development/Configuration/JPA/orm.xml
orm.xml
Use the orm.xml file to apply the metadata to the persistence unit. This metadata is a union of all the mapping files and the annotations (if there is no xml-mapping-metadata-complete element). If you use one mapping orm.xml file for your metadata and place this file in a META-INF directory on the classpath, then you do not need to explicitly list it. The EclipseLink persistence provider will automatically search for this file (orm.xml)and use it.
If you use a different name for your mapping files, or place them in a different location, you must list them in the mapping-file element of the persistence.xml file, as shown here:
<persistence-unit name="EmployeeService"> <jta-data-source>jdbc/EmployeeServiceDS</jta-data-source> <mapping-file>META-INF/employee_service_queries.xml</mapping-file> </persistence-unit>
Note: In this example, the orm.xml file is not listed -- the persistence provider finds it by default.
Advantages and Disadvantages of Using XML
Some advantages of using XML instead of Annotations include:
- No coupling between the metadata and the source code
- Compliance with the existing, pre-EJB 3.0 development process
- Support in IDEs and source control systems
The main disadvantages of mapping with XML include:
- Its inherent complexitiy (when compared to annotations)
- The need for replication of the code context
